The studies described in the present proposal are designed to explore the conceptual basis of the infant's perception of facial expression. The need for such work is critical if we are to understand the important role the face plays in the communication of affect prior to the onset of language. Two experiments are described herein that speak to the issue of whether infants are able to categorize the expressions happy and fear when these expressions vary along two dimensions: a) person posing the expression, and b) the intensity of the expression (e.g., mild or very happy). Using a paired-comparison procedure, 4-, 7-, and 8-month-old infants in the first experiment will be tested on their ability to discriminate and generalize their discrimination of a within-category change of either a happy or fear facial expression (i.e., can they discriminate a female face posing a mild-happy expression from the same face posing a very-happy expression, and can they generalize such discrimination across four different female faces?) Using the same procedure, a second experiment will explore the 4-, 7-, and 8-month-old infant's ability to discriminate and generalize their discrimination of a happy vs. fear facial expression (i.e., a between-category discrimination), when these expressions range in intensity (mild vs. very) and model (4 females). It is hoped that from such work our knowledge of the infant's perception of facial expressions will be greatly improved. In future work these findings will be extended to : a) infants born to parents who provide misleading or erroneous affective information (e.g., those suffering from affective disorders), and b) infants viewing faces of chimpanzees posing a variety of facial expressions. While different in conception, both studies are designed to explore the infant's ability to perceive affect.